Process for making load limiting yarn

ABSTRACT

The present invention provides a yarn having a force-displacement profile such that:  
     (a) when the yarn is subjected to an initial stress barrier of from about 0.8 gram/denier to less than or equal to about 1.2 grams/denier, the yarn elongates to less than 5 percent and has an initial modulus in the range from about 30 grams/denier to about 80 grams/denier;  
     (b) upon subjecting the yarn to greater than the initial stress barrier and to less than or equal to about 1.5 grams/denier, the yarn elongates further to at least about 8 percent; and  
     (c) upon subjecting the yarn to greater than 1.5 grams/denier, the modulus increases sharply and the yarn elongates further until the yarn breaks at a tensile strength of at least about 6 grams/denier, wherein the yarn comprises a multiplicity of fibers, all of the fibers have substantially the same force-displacement profile, and are made from polymers having a glass transition temperature in the range from about −40° C. to about +70° C.  
     The present invention also provides a process for making block copolymer and a process for making load limiting yarn from the block copolymer.  
     Webbing from the present yarn is useful for seat belts, parachute harnesses and lines, shoulder harnesses, cargo handling, safety nets, trampolines, safety belts or harnesses for workers at high attitudes, military arrestor tapes for slowing aircraft, ski tow lines, and in cordage applications such as for yacht mooring or oil derrick mooring.

BACKGROUND OF THE INVENTION

[0001] A typical vehicle safety seat belt system is designed to restrictthe displacement of an occupant with respect to the occupant's seatedposition within the vehicle when the vehicle experiences a sudden, sharpdeceleration. (See U.S. Pat. No. 3,322,163). A typical seat belt hasthree main portions: the retractor belt, the torso belt, and the lapbelt and the performance of each belt may be characterized by itsforce-displacement curve. The area under the force-displacement curve isreferred to as the energy absorbed by the safety restraint.

[0002] Current vehicle safety seat belts are made from fully drawnpolyethylene terephthalate (“PET”) fiber which is partially relaxed(2.7%) and having a tenacity of at least 7.5 grams/denier and 14%elongation at break. U.S. Government regulation requires that seat beltsmust withstand loads up to 6,000 lbs. However, a problem exists with thecurrent PET fiber based seat belts. Crash studies indicate that afterthe initial vehicle impact occurs (e.g. at a speed of about 35miles/hour), the occupant tends to move forward from his seated positionuntil the belt engages to build restraining forces. As indicated in FIG.1, the relatively unyielding belt made from PET fiber exerts a force ofat least 2000 pounds (about 9000 Newtons) against the occupant at theseat belt torso position so as to cause the occupant to have high chest,rib cage, head, neck, and back injuries when the occupant rebounds andimpacts the back structure of the seat assembly.

[0003] When a car collides at a speed of 35 miles/hour, an impact energyto which an average sized person in the car is subjected is at least 500Joules on the torso belt. Although the current PET fiber may absorb theimpact energy, damage to the vehicle occupant still occurs due to theundesirable fiber force-displacement curve. In 70 milliseconds, anaverage sized passenger will experience high forces of up to 2,000pounds (about 9,000 Newtons) as shown in FIG. 1.

[0004] In order to absorb the impact energy and to reduce the seat beltload against the vehicle occupant, U.S. Pat. No. 3,550,957 discloses ashoulder harness having stitched doubled sections of the webbingarranged above the shoulder of the occupant so that the stitchingpermits the webbing to elongate from an initial length toward a finallength at a controlled rate under the influence of a predeterminedrestraining force. However, the stitched sections do not give thedesirable amount of energy absorption, do not provide uniform response,and are not reusable in multiple crashes. See also U.S. Pat. No.4,138,157.

[0005] U.S. Pat. No. 3,530,904 discloses a woven fabric which isconstructed by weaving two kinds of yarns having relatively differentphysical properties and demonstrates energy absorption capability. U.S.Pat. Nos. 3,296,062; 3,464,459; 3,756,288; 3,823,748; 3,872,895;3,926,227; 4,228,829; 5,376,440; and Japanese Patent 4-257336 furtherdisclose webbings which are constructed of multiple kinds of warp yarnshaving different tenacity and elongations at break. DE 19513259A1discloses webbings which are constructed of short warp threads whichwill absorb the initial tensile load acting on the webbing and alsolonger warp threads which will absorb the subsequent tensile load actingon said webbing.

[0006] Those skilled in this technical area have recognized thedeficiencies in using at least two different yarn types as taught by thepreceding references. U.S. Pat. No. 4,710,423 and Kokai PatentPublication 298209 published on Dec. 1, 1989 (“Publication 298209”)teach that when using at least two different yarn types, energyabsorption occurs in a stepwise manner and thus, the web does not absorbthe energy continuously and smoothly. Therefore, after one type of warpsabsorbs a portion of the impact energy, and before another type of warpsabsorbs another portion of the impact energy, the human body is exposedto an undesirable shock.

[0007] UK Patent 947,661 discloses a seat belt which undergoes anelongation of greater than or equal to 33 percent when subjected to atleast 70% of the breaking load. This reference does not teach or suggestthe present load limiting yarn.

[0008] U.S. Pat. No. 3,486,791 discloses energy absorbing devices suchas a rolled up device which separates a slack section of the belt fromthe taut body restraining section by clamping means which yield under apredetermined restraining force to gradually feed out the slack sectionso that the taut section elongates permitting the restrained body tomove at a controlled velocity. The reference also describes a devicewhich anchors the belt to the vehicle by an anchor member attached tothe belt and embedded in a solid plastic energy absorber. These kinds ofmechanical devices are expensive, are not reusable, provide poor energyabsorption, and are difficult to control. An improvement on the forgoingdevices is taught by U.S. Pat. No. 5,547,143 which describes a loadabsorbing retractor comprising: a rotating spool or reel, seat beltwebbing secured to the reel; and at least one movable bushing,responsive to loads generated during a collision situation, fordeforming a portion of the reel and in so doing dissipating a determinedamount of the energy. This kind of mechanical device is built-in with aspecific amount of load limiting and energy absorption towards certainsized occupants, and cannot be adjusted to the needs of different sizedoccupants in real transportation scenario. Furthermore, this kind ofmechanical device is not reusable to limit the load in multiple crashessince the reel is deformed permanently in the first vehicle collision.

[0009] U.S. Pat. No. 4,710,423 and Publication 298209 disclose webbingcomprised of relaxed polyethylene terephthalate (“PET”) yarns havingtenacity of at least 4 grams/denier and an ultimate elongation of from50% to 80%. Due to the inherent physical properties of PET yarn (e.g.glass transition temperature 75° C.), the examples of U.S. Pat. No.4,710,423 and Publication 298209 show that, at 5% elongation, the loadhas already reached more than 1500 lbs (about 6,700 Newtons). The damageto the occupant by the seat belt still exists and thus, the beltmaterial needs to be further modified. Examples in these two patentsalso show that if PET yarn is overrelaxed, the yarn tenacity drops to2.3 grams/denier.

[0010] Kokai Patent Publication 90717 published on Apr. 4, 1995discloses high strength polybutylene terephthalate homopolymer (“PBT”)fiber based energy absorption webbing. The fiber's tenacity is over 5.8grams/denier, breaking elongation is over 18.0%, and the stress at 10%elongation is less than 3.0 grams/denier. However, this reference failsto teach PBT fiber demonstrating the initial stress requirement whichengages the seat belt to protect the occupant and the means to controlthe initial stress barrier. A low initial stress barrier of yarn resultsin a low knuckle force point of the finished seat belt which allowsexcessive excursion of occupant and leads to serious injuries.

[0011] It would be desirable to have an improved energy absorbing seatbelt, which has a smoother performance than that of the known stitchedwebbing approach or the known use of at least two different fibers, isreusable in multiple crashes unlike the known mechanical clamp anddevice approach, and also addresses the ability to control the initialstress barrier and the impact energy absorption from different sizedvehicle occupants.

[0012] The present inventors in commonly assigned US patent applicationSer. No. 08/788,895 filed Apr. 18, 1997 and allowed U.S. patentapplication Ser. No. 08/819,931 filed Mar. 18, 1997 have responded tothe foregoing need. Also see T. Murphy, “Buckling Up for the Future”,WARD's Auto World, 95 (1997).

SUMMARY OF THE INVENTION

[0013] The present invention also responds to the foregoing need in theart by providing load limiting yarn, a process for making the loadlimiting yarn, and webbing made from the load limiting yarn. Thewebbing, if used as seat belt to restrain occupant, demonstrates energyabsorption and load limiting performance. This type of load limitingseat belt comprises yarn which has a force-displacement profilecharacterized by:

[0014] (a) when the yarn is subjected to an initial stress barrier offrom about 0.8 gram/denier to less than or equal to about 1.2grams/denier, the yarn elongates to less than 5 percent and has aninitial modulus in the range from about 30 grams/denier to about 80grams/denier;

[0015] (b) upon subjecting the yarn to greater than the initial stressbarrier and to less than or equal to about 1.5 grams/denier, the yarnelongates further to at least about 8 percent; and

[0016] (c) upon subjecting the yarn to greater than 1.5 grams/denier,the modulus increases sharply and the yarn elongates further until theyarn breaks at a tensile strength of at least about 6 grams/denier,wherein the yarn comprises a multiplicity of fibers, all of the fibershave substantially the same force-displacement profile, and are madefrom polymers having a glass transition temperature in the range fromabout −40° C. to about +70° C.

[0017] The term “modulus” as used herein means the slope of theforce-displacement curve.

[0018]FIG. 2 illustrates the force-displacement profile of the InventiveExample. The initial stress barrier is indicated as ISB on FIG. 2. Thepresent webbing comprised of this type of yarn is advantageous becausethe present webbing has better impact energy absorption and a smootherperformance than that of the known stitched webbing approach or theknown use of at least two different fibers, is reusable unlike the knownmechanical device, and also addresses the ability to control the initialstress barrier and the impact energy absorption.

[0019] The present invention also provides a process for making loadlimiting yarn comprising making block copolymer and then spinning theblock copolymer into yarn. The present invention for making a blockcopolymer useful in the present load limiting yarn occurs in a twinscrew extruder comprises the steps of:

[0020] (A) forwarding aromatic polyester melt to an injection positionin the twin screw extruder wherein the aromatic polyester has:

[0021] (i) an intrinsic viscosity which is measured in a 60/40 by weightmixture of phenol and tetrachloroethane and is at least about 0.6deciliter/gram and

[0022] (ii) a Newtonian melt viscosity which is calculated to be atleast about 7,000 poise at 280°C.;

[0023] (B) injecting lactone monomer into the molten aromatic polyesterfrom step (A);

[0024] (C) dispersing the injected lactone monomer into the aromaticpolymer melt so that a uniform mixture forms in less than about thirtyseconds; and

[0025] (D) reacting the uniform mixture resulting from step (C) at atemperature from about 250° C. to about 280° C. to form a blockcopolymer. All of steps (A) to (D) occur in less than about four minutesresidence time in the twin screw extruder.

[0026] The present process is advantageous because high IV startingaromatic polyester can be used and the short reaction time at hightemperature results in block copolymer with minimum transesterification,a high melting point, and a high melt viscosity. Preferably, the blockcopolymer has a melting point of at least about 220° C.

[0027] Preferably, the block copolymer melt is then in step (E)devolatilized in the twin screw extruder to remove the residual lactonemonomer. Preferably, after the devolatization, ultraviolet absorbers,antioxidants, pigments, and other additives are then in step (F)injected and dispersed into the copolymer melt in the twin screwextruder.

[0028] The block copolymer is then forwarded from the twin screwextruder to a fiber spinning equipment. The present process for makingfiber from the block copolymer comprises the steps of:

[0029] (G) from the twin screw extruder, metering the block copolymermelt at a temperature from about 240° C. to about 280° C. into a spinpot and extruding filaments from the spin pot;

[0030] (H) passing the extruded filaments through a heated sleeve havinga temperature from about 200° C. to about 300° C.;

[0031] (I) cooling the filaments with ambient air wherein the air flowsperpendicularly to the filament direction at a flow rate of at leastabout 0.1 meter per second;

[0032] (J) applying a spin finish to the cooled filaments;

[0033] (K) taking up the filaments to form yarn on a first roll;

[0034] (L) passing the yarn to a second roll having a temperature fromgreater than the yarn's glass transition temperature to less than theyarn's crystallization temperature;

[0035] (M) drawing the yarn between said second roll and draw rolls overa heated shoe or in a draw point localizer which is positioned betweensaid second roll and draw rolls and has a temperature from about 180° C.to about 350° C. and then annealing the drawn yarn on said draw rollshaving a temperature from about 140° C. to about 200° C.;

[0036] (N) relaxing the drawn yarn between said draw rolls and a finalroll so that the relaxed yarn has a shrinkage of about 7 percent toabout 20 percent;

[0037] (O) cooling the relaxed yarn on the final roll set at roomtemperature; and

[0038] (P) winding up the cooled yarn.

[0039] The above process for making block copolymer in a twin screwextruder and spinning load limiting yarn may be carried out in acontinuous process from the block copolymerization to the final wound-upyarn or in a discontinuous process where the block copolymer is preparedin the twin screw extruder and chipped and the copolymer chips are thenspun from a single screw extruder into load limiting yarn.

[0040] Other advantages of the present invention will be apparent fromthe following description, attached drawings, and attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 illustrates the performance (with load as a function oftime) of a known poly(ethylene terephthalate) homopolymer seat belt atthe torso position in a vehicle collision.

[0042]FIG. 2 illustrates a stress-strain curve of the yarn of thepresent invention.

[0043]FIG. 3 illustrates twin screw extruder configuration useful in thepresent process.

[0044]FIG. 4 illustrates the present fiber spin-draw-relax process.

[0045]FIG. 5 illustrates the performance (with load as a function oftime) of the load limiting seat belt of the present invention at thetorso position in a vehicle collision.

DETAILED DESCRIPTION OF THE INVENTION

[0046] The present yarn has the following force-displacement profile.

[0047] (a) When the yarn is subjected to an initial stress barrier offrom about 0.8 gram/denier to less than or equal to about 1.2grams/denier, the yarn elongates to less than 5 percent and preferably,to less than 3 percent. The yarn has an initial modulus in the rangefrom about 30 grams/denier to about 80 grams/denier and the preferredinitial modulus ranges from about 40 grams/denier to about 60grams/denier. The yarn's initial high modulus and the height of theinitial stress barrier are needed to engage the seat belt and ensurethat all the occupant collision energy will be absorbed under thesubsequent load limiting portion of the force-displacement curve.

[0048] (b) Upon subjecting the yarn to greater than the initial stressbarrier and less than or equal to about 1.5 grams/denier, the yarnelongates further to at least about 8 percent. Preferably, the yarnelongates to at least about 10 percent. This portion of theforce-displacement curve is the yarn's load limiting portion whichabsorbs collision energy and prevents the passenger from experiencingexcessive loads.

[0049] (c) Upon subjecting the yarn to greater than 1.5 grams/denier,the modulus increases sharply and the yarn elongates further until theyarn breaks at a tensile strength of at least about 6 grams/denier. Theyarn comprises a multiplicity of fibers and all of the fibers havesubstantially the same force-displacement profile. The term“multiplicity of fibers” as used herein means at least 100 filaments areused for each end of seat belt yarn. In a seat belt webbing comprisingat least 300 ends of the foregoing yarn, the load on the passenger'storso position may be reduced to as low as 450 lbs (about 2,000 Newtons)even at a collision speed of 35 miles/hour. The reduced force thenminimizes or eliminates potential damage to the vehicle occupant.

[0050] The yarn is made from a polymer having a glass transitiontemperature in the range from about −40° C. to about +70° C., preferablyabout −20° to about +60°C., and more preferably about +35° C. to about+55° C. The polymer may be a homopolymer, random copolymer, diblockcopolymer, triblock copolymer, or segmented block copolymer.

[0051] Examples of preferred homopolymers include polytrimethyleneterephthalate; polyisobutylene terephthalate; and long chain alkyleneterephthalates and naphthalate polymers.

[0052] Examples of preferred random copolyesters include copolyesterwhich, in addition to the ethylene terephthalate unit, containcomponents such as ethylene adipate, ethylene sebacate, or other longchain alkylene terephthalate units. This component is present in anamount greater than 10 percent.

[0053] Examples of preferred block copolymers include diblock, triblock,and segmented block structure. Block copolymers comprise at least onehard crystalline aromatic polyester block and at least one softamorphous aliphatic polyester block. The crystalline aromatic polyesterincludes the homopolymers such as polyethylene terephthalate (“PET”);polytrimethylene terephthalate; polybutylene terephthalate;polyisobutylene terephthalate; poly(2,2-dimethylpropyleneterephthalate); poly[bis-(hydroxymethyl )cyclohexene terephthalate];polyethylene naphthalate (“PEN”); polybutylene naphthalate;poly[bis-(hydroxymethyl)cyclohexene naphthalate]; other polyalkylene orpolycycloalkylene naphthalates and the mixed polyesters which, inaddition to the ethylene terephthalate unit, contain component such asethylene isophthalate; ethylene adipate; ethylene sebacate;1,4-cyclohexylene dimethylene terephthalate; or other long chainalkylene terephthalate units. Commercially available aromatic polyestersmay be used. A mixture of aromatic polyesters may also be used. The morepreferred aromatic polyesters include PET and PEN.

[0054] Preferably, the amorphous aliphatic polyester block is made fromlactone monomer. Preferred lactone monomers include ε-caprolactone,propiolactone, butyrolactone, valerolactone, and higher cyclic lactones.The most preferred lactone monomer is ε-caprolactone. Commerciallyavailable lactone monomers may be used. Two or more types of lactonesmay be used simultaneously.

[0055] Preferably, the aromatic polyester has: (i) an intrinsicviscosity which is measured in a 60/40 by weight mixture of phenol andtetrachloroethane at 25° C. and is at least about 0.6 deciliter/gram and(ii) a Newtonian melt viscosity which is calculated to be at least about7,000 poises at 280° C. The intrinsic viscosities, as measured in a60/40 by weight mixture of phenol and tetrachloroethane, of thepreferred aromatic polyesters are about 0.8 for PET and about 0.6 forPEN. The more preferred IV for PET is 0.9 and for PEN is 0.7. TheNewtonian melt viscosity of PET (with an IV=1) is calculated to be about16,400 poise at 280° C. and the Newtonian melt viscosity of PEN (with anIV=1) is greater than PET's melt viscosity.

[0056] For use in load limiting seat belts, the PET-polycaprolactoneblock copolymer may have a polycaprolactone concentration of preferablyabout 10 to about 30 weight percent. In the block copolymer, thepolycaprolactone concentration may be varied to achieve the desiredinitial stress barrier and impact energy absorption with load limitingperformance.

[0057] The present process for making a block copolymer useful in thepresent load limiting yarn occurs in a twin screw extruder and comprisesthe steps of:

[0058] (A) forwarding aromatic polyester melt to an injection positionin a twin screw extruder wherein the aromatic polyester melt has

[0059] (i) an intrinsic viscosity which is measured in a 60/40 by weightmixture of phenol and tetrachloroethane and is at least about 0.6deciliter/gram and

[0060] (ii) a Newtonian melt viscosity which is calculated to be atleast about 7,000 poise at 280° C.;

[0061] (B) injecting lactone monomer into the molten aromatic polyesterof step (A);

[0062] (C) dispersing the injected lactone monomer into the aromaticpolymer melt so that a uniform mixture forms in less than about thirtyseconds; and

[0063] (D) reacting the uniform mixture resulting from step (C) at atemperature from about 250° C. to about 280° C. to form a blockcopolymer. All of steps (A) to (D) occur in less than about four minutesresidence time in the twin screw extruder.

[0064] Step (A) for making the block copolymer in a twin screw extrudercomprises forwarding aromatic polyester melt to an injection position.The aromatic polyester is added to the twin screw extruder. The aromaticpolyester may be molten and then fed by a melt metering pump to the twinscrew extruder or the aromatic polyester may be fed in pellet form fedby a “weight in loss” feeder to the twin screw extruder and then meltedin the twin screw extruder. As those skilled in the art know, a weightin loss feeder has a hopper filled with pellets and the feeding rate iscontrolled by weight loss of pellets from the hopper. If aromaticpolyester melt from a reactor is used as the starting material,intermeshing close conveying elements may be used to forward the meltdownstream. If aromatic polyester pellets are used as the startingmaterial, preferably intermeshing open, open to close, and closeconveying elements are assembled under the feeding position in the twinscrew extruder to melt the pellets and to forward the melt downstream tothe injection position.

[0065] We have found that by using a twin screw extruder, mixing andreaction of the aromatic polyester melt with the lactone monomer havinga drastic viscosity difference become feasible. Useful twin screwextruders are commercially available; however, the mixing elements andthe element arrangement sequence thereof in the twin screw extruderneeded for the present invention are critical and are described below.Preferred twin screw extruders are intermeshing twin screw extruders.FIG. 3 illustrates one of the preferred intermeshing twin screwextrusion processes used in the present invention. A single screwextruder such as taught by U.S. Pat. No. 4,045,401 is not useful in thepresent invention because a single screw extruder does not provide thefast mixing, residence time, residence time distribution, meltagitation, and process control required for the present invention.

[0066] The initial extrusion temperature exceeds the melting point (asmeasured by Perkin-Elmer Differential Scanning Calorimeter (DSC) fromthe maxima of the endotherm resulting from scanning a 2 milligram sampleat 20° C. per minute) of the aromatic polyester used. The melting pointsof the preferred aromatic polyesters are 250° C. for PET and 266° C. forPEN. The preferred initial extrusion zone temperature is at least about30° C. above the aromatic polyester melting point. Thus, the preferredinitial extrusion temperature for PET is at least about 280° C. whilethe preferred initial extrusion temperature for PEN is at least about296° C.

[0067] Step (B) for making the block copolymer comprises injectinglactone monomer into the molten aromatic polyester from step (A).Preferably, a piston pump is used to inject the lactone monomer at aconstant rate into the aromatic polyester melt.

[0068] Preferably, the lactone monomer is premixed with catalysts atroom temperature. Commercially available catalysts may be used.Preferred catalysts are organometallics based on metals such as lithium,sodium, potassium, rubidium, cesium, magnesium, inorganic acid salts,oxides organic acid salts and alkoxides of calcium, barium, strontium,zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony,arsenic, cerium, boron cadmium and manganese; and their organometalliccomplexes. More preferred catalysts are organic acid salts andorganometallic compounds of tin, aluminum, and titanium. The mostpreferred catalysts are tin diacylate, tin tetra acylate, dibutyltinoxide, dibutyltin dilaurate, tin octonate, tin tetra acetate,triisobutyl aluminum, aluminum acetylacetonate, aluminum isopropoxide,aluminum carboxylates, tetra butyl titanium, germanium dioxide, antimonytrioxide, prophyrin and phthalocyanine complexes of these metal ions.Two or more catalyst types may be used in parallel. Preferably, theamount of catalyst used is about 0.01 to about 0.2 weight percent basedon the combined weight of aromatic polyester and lactone monomer.

[0069] Step (C) for making the block copolymer comprises dispersing theinjected lactone monomer into the aromatic polymer melt so that auniform mixture forms in less than about thirty seconds and preferably,in less than about twenty seconds. The phrase “uniform mixture” as usedherein means even distribution of the lactone monomer into the aromaticpolyester melt. Preferably, distributive combing mixers are used todisperse the injected lactone monomer into the high melt viscosityaromatic polyester melt. This rapid uniform mixture formation results inuniform ring opening polymerization of lactone, uniform block copolymerproduct, and stable downstream process. Preferably, at least one forwarddistributive intermeshing combing mixer, at least one neutraldistributive intermeshing combing mixer, and at least one reversedistributive intermeshing combing mixer are used to achieve the desiredmixing.

[0070] Step (D) for making the block copolymer comprises reacting theuniform mixture resulting from step (C) at a temperature from about 250°C. to about 280° C. to form block copolymer in less than about fourminutes. The mixture is forwarded further downstream into a reactionzone where turbulators, mixers, and conveying elements are assembled.Turbulators are used to continuously agitate the melt, increase extrudervolume without sacrificing the throughput rate, and control the reactiontime. The hydroxyl end group of the aromatic polyester initiatesring-open polymerization of lactone monomer under catalytic conditionsto form lactone block at the end of the aromatic polyester. The melt isconstantly agitated by the turbulators and mixing elements to homogenizethe reaction. This short reaction time minimizes transesterificationwhile ensuring complete reaction which means to polymerize the lactonemonomer to form the block at the aromatic polyester chain end andcomplete consumption of the injected lactone monomer. To determineresidence time and residence distribution time, we added colored pelletswhich served as a marker to the aromatic polyester pellets. The term“residence time” means the time period starting from the colored pelletaddition to the strongest color appearance. The term “residencedistribution time” means the time range starting from the colorappearance and ending at color disappearance. As the residencedistribution time decreases, product uniformity increases. The residencedistribution time is preferably less than about three minutes and morepreferably less than about one minute. Preferably, the degree oftransesterification between aromatic polyester and lactone blocks isless than five weight percent of the combined material weight.

[0071] Preferably, the block copolymer melt is then in step (E)devolatilized under vacuum in the twin screw extruder to remove theresidual lactone monomer. The devolatization element allows theformation of thin polymer melt film and high surface area for effectiveremoval of volatiles.

[0072] Preferably, after the devolatization, ultraviolet absorbers,antioxidants, pigments, and other additives are then in step (F)injected and dispersed into the copolymer melt in the twin screwextruder by a piston pump or a gear pump at a constant rate. The forwarddistributive intermeshing combing mixers are used to homogenize theadditives in the copolymer. The melt in the temperature range of about240° C. to about 280° C. is then forwarded downstream to a melt meteringpump for fiber spinning.

[0073] Preferred ultraviolet absorbers are stabilizers based onbenzophenones, benzotriazoles, triazines, and oxanilides. The mostpreferred ultraviolet absorbers are2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxy phenol;2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-octyloxy phenol;2-(2H-benzotriazol-2-yl)-p-cresol;2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol;2-ethoxy-2′-ethyloxanilide; 5-tert-butyl-2-ethoxy-2′-ethyloxanilide;propanedioic acid; [(4-methoxyphenyl)-methylene]-; and bis(1,2,2,6,6-pentamethyl-4-piperidinyl) ester. Two or more stabilizertypes may be used in parallel. Preferably, the amount of ultravioletabsorber used is about 0.1 to about 2 weight percent based on thecombined weight of aromatic polyester and lactone monomer.

[0074] Preferred antioxidants are additives based on hindered phenolics,hindered benzoates, hinder amines, and phosphites/phosphonites. The mostpreferred antioxidants aretetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane;triethyleneglycol bis[3-(3′-tert-butyl-4′-hydroxy-5′-methylphenyl)propionate]; 1,6-hexanediamine,N,N′-bis(2,2,6,6-tetramethyl-4′-piperidinyl)-,polymer withmorpholine-2,4,6-trichloro-1,3,5-triazine; andtris(2,4-di-tert-butylphenyl) phosphite. Two or more additive types maybe used. Preferably, the amount of antioxidant used is about 0.1 toabout 1 weight percent based on the combined weight of aromaticpolyester and lactone monomer.

[0075] The block copolymer is then forwarded from the twin screwextruder to the fiber spinning equipment. The present process for makingload limiting yarn from the block copolymer comprises the steps of:

[0076] (G) from the twin screw extruder and through a melt meteringpump, metering the block copolymer melt at a temperature from about 240°C. to about 280° C. into a spin pot and extruding filaments from thespin pot equipped with a spinnerette;

[0077] (H) passing the extruded filaments through a heated sleeve havinga temperature from about 200° C. to about 300° C.;

[0078] (I) cooling the filaments with ambient air wherein the air flowsperpendicularly to the filament direction and at a flow rate of at leastabout 0.1 meter per second;

[0079] (J) applying a spin finish to the cooled filaments;

[0080] (K) taking up the filaments to form yarn on a first roll;

[0081] (L) passing the yarn to a second roll having a temperature fromgreater than the yarn's glass transition temperature to less than theyarn's crystallization temperature;

[0082] (M) drawing the yarn between said second roll and draw rolls overa heated shoe or in a draw point localizer which is positioned betweensaid second roll and draw rolls and has a temperature from about 180° C.to about 350° C. and then annealing the drawn yarn on said draw rollshaving a temperature from about 140° C. to about 200° C.;

[0083] (N) relaxing the drawn yarn between said draw rolls and a finalroll so that the relaxed yarn has a shrinkage of about 7 percent toabout 20 percent;

[0084] (P) cooling the relaxed yarn on the final roll set at roomtemperature; and

[0085] (Q) winding up the cooled yarn.

[0086] The above process for making block copolymer in a twin screwextruder and spinning load limiting yarn may be carried out in acontinuous process from the block copolymerization to the final wound-upyarn or in a discontinuous process where the block copolymer is preparedin the twin screw extruder and chipped and the copolymer chips are thenspun from a single screw extruder into load limiting yarn.

[0087]FIG. 4 illustrates the present process for manufacturing loadlimiting yarn with a specific type of stress-strain curve (FIG. 2). Theprocess consists of block copolymerization in the twin screw extruder,melt spinning, filament cooling, yarn drawing, relaxing, and windingsteps.

[0088] In step (G) which is the first step for making load limiting yarnfrom the block copolymer, the melt at a temperature from about 240° C.to about 280° C. is fed through a metering pump into a spin pot which iscomprised of filtration screens and a spinnerette. Preferably, thepolymer throughput rate through the spinnerette is in the range fromabout 1.5 grams/hole/minute to about 3.5 grams/hole/minute and thespinning temperature is in the range from about 240° C. to about 280° C.Preferably, the melt viscosity of PET-Polycaprolactone copolymer underthese spinning conditions, e.g., spinning temperature and shear rate, isbetween about 2,000 to about 4,000 poise. Filaments are extruded fromthe spin pot.

[0089] In steps (H) and (I), the extruded filaments pass through aheated sleeve having a temperature from about 200° C. to about 300° C.and are then cooled by ambient air flowing perpendicular to the filamentdirection at a flow rate of at least about 0.1 meter/second. Ambient airhas a temperature from about 10° C. to about 30° C. The propertemperature of the heated sleeve and adequate air flow rate areimportant for achieving the needed yarn and filament uniformity. Yarnuniformity is measured by uster method which indicates yarn denierconsistency. Filament uniformity is measured by radial birefringencemethod which indicates the degree of molecular orientation in bothsurface and core of the filaments. Prior to take-up, a spin finish isapplied in step (J) to the quenched or cooled filaments by a finishapplicator. Preferably, the applied spin finish is based on a watersoluble low molecular weight polymer which may be efficiently removed bydissolving it in water.

[0090] In step (K), the quenched or cooled filaments are taken up by afirst roll to obtain as-spun yarn with low molecular orientation andminimum crystallinity. The phrase “low molecular orientation” as usedherein preferably means that the radial birefringence is less than about0.01. The phrase “minimum crystallinity” as used herein preferably meansthat the crystallinity is less than about 5 percent. In step (I), theyarn is then fed onto a second roll having a temperature from greaterthan the yarn's glass transition temperature (“Tg”) to less than theyarn's crystallization temperature (“Tc”). The glass transitiontemperature of PET-polycaprolactone copolymer varies between about 35°C. to about 55° C., depending upon the weight percent of ε-caprolactonein the polymer and block transesterification. The crystallizationtemperature of PET-polycaprolactone copolymer varies between about 100°C. to about 170° C., depending upon the weight percent of ε-caprolactonein the polymer and the degree of transesterification. The purpose ofthis heating is to preheat the yarn.

[0091] In step (M), the preheated yarn is drawn between the second rolland draw rolls over a heated shoe or in a draw point localizer which ispositioned between the second roll and draw roll and has a temperaturefrom about 180° C. to about 350° C. and then annealing the drawn yarn onthe draw rolls having a temperature from about 140° C. to about 200° C.The purpose of the heated shoe or draw point localizer is to furtherheat the yarn and localize the drawing of the yarn. The hot media in thedraw point localizer may be air or steam. Draw rolls having atemperature between about 140° C. to about 200° C. are used to promotecrystallization and annealing of the yarn. Preferably, the yarn is drawnwith at least 6:1 draw ratio. The time for the annealing of drawn yarnis less than about one second.

[0092] In step (N), the drawn yarn is relaxed between the draw rolls anda final roll with a controlled shrinkage set by the speed difference ofthe rolls and the temperature of the draw rolls from which the yarn isrelaxed. Preferably, the degree of shrinkage is between about 7% toabout 20% to yield the yarn with desired stress-strain curve. The finalroll is set at room temperature. In steps (O) and (P), the relaxed yarnis cooled and wound-up on a winder set at room temperature and at thespeed of the final roll.

[0093] Seat belts are usually woven with a warp yarn of about 1000 toabout 1500 denier and a breaking strength of at least about 5grams/denier and weft yarn with a denier of about 200 to about 900 and abreaking strength of at least about 5 grams/denier. Weaving conditionsare selected in order for the seat belt to preserve the stress/strainproperties of the yarn and maintain the webbing strength. Our resultsindicate that the most commonly used 2×2 twill weaving pattern may besuccessfully used for load limiting seat belts. The seat belt webbing isdyed in a thermosol equipment at a temperature between about 100° C. toabout 180°C. The automotive collision tests at 35 miles per hour of thistype of load limiting seat belt show force against occupant is reducedto 800 lbs (3.6 KN)˜1,600 lbs (7.2 KN) and injury criteria areminimized.

[0094] The present webbing provides the desired load limitingcharacteristics in the absence of a clamping device such as taught byU.S. Pat. No. 3,486,791; stitching such as taught by U.S. Pat. No.3,550,957; and a mechanical energy absorbing device such as the constantforce retractor taught by U.S. Pat. No. 5,547,143. The present webbingand yarn provide the desired load limiting characteristics and are madefrom material other than the PBT homopolymer taught by Publication90717. The present webbing provides the desired load limitingcharacteristics by using warp yarns having substantially the sameforce-displacement profile instead of the plurality of warp yarnforce-displacement profiles taught by U.S. Pat. Nos. 3,756,288;3,823,748; 3,872,895; 4,288,829; and 5,376,440. The present webbingprovides the desired load limiting characteristics and is made frompolymer other than the PET homopolymer taught by U.S. Pat. No. 4,710,423and Publication 298209.

[0095] The present web is useful for seat belts, parachute harnesses andlines, shoulder harnesses, cargo handling, safety nets, trampolines,safety belts or harnesses for workers at high attitudes, militaryarrestor tapes for slowing aircraft, ski tow lines, and in cordageapplications such as for yacht mooring or oil derrick mooring.

TEST METHODS

[0096] In the following Examples, the reduced specific viscosity wasdetermined as follows. Solution viscosity and solvent viscosity weremeasured and specific viscosity was calculated by (solutionviscosity-solvent viscosity)/(solvent viscosity). Reduced specificviscosity was calculated from specific viscosity/solution concentration.

[0097] The intrinsic viscosity of polymer was determined by plotting thereduced specific viscosity of polymer solution versus solutionconcentration in a mixed solvent of 60 parts of phenol and 40 parts oftetrachloroethane at 25° C. The intercept was the intrinsic viscosity ofpolymer. It is understood that IV is expressed in units of decilitersper gram or (dl/g) herein even if such units are not indicated.

[0098] Thermal properties were measured by Perkin Elmer DifferentialScanning Calorimetry-7 using a polymer chip sample size of about fivemilligrams, heating the sample to 285° C. at the rate of 10° C./minute,holding the sample at 285° C. for two minutes, and cooling the sample to30° C. at the rate of 10°C./minute. The peak temperature of endotherm inheating scan was the melting point of a polymer and the peak temperatureof exotherm in cooling scan was the crystallization temperature of apolymer. The glass transition temperature of a polymer was the secondorder thermal transition temperature during both heating and coolingscans.

[0099] For the preferred yarn made of block copolymer, the Newtonianmelt viscosity for the starting PET of the Inventive Example wascalculated to be at least 7,000 poise at 280° C. based on AndrzejZiabicki, “Effects of Molecular Weight on Melt Spinning and MechanicalProperties of High-Performance Poly(ethylene Terephthalate) Fibers”,Textile Res. J. 66(11), 705-712 (1996) and A. Dutta, “IdentifyingCritical Process Variables in Poly(ethylene Terephthalate) MeltSpinning”, Textile Res. J. 54, 35-42 (1984). The Newtonian meltviscosity means the melt viscosity at zero shear rate.

[0100] Melt viscosity of block copolymer under various spinningconditions was extrapolated from melt rheology data obtained fromKayeness Galaxy V capillary rheometer with capillary die L/D=30:1 usingshear rates ranging from 50/sec to 998/sec. The samples were dried at160° C. for 16 hour under vacuum before measurement. 15 gram of samplewas packed into the rheometer and allowed to melt to reach temperatureequilibrium for 6 minutes before beginning melt viscosity measurements.Runs under different temperature were made at constant shear rate over arange of shear rates including 50 sec⁻¹, 100 sec⁻¹, 200 sec⁻¹, 499sec⁻¹, and 998 sec⁻¹ and at times up to 20 minutes. No corrections weremade for end effects so values are apparent melt viscosities.

[0101] Radial birefringence was determined by using an Ausjenainterference microscope to measure the radial structure through acorrect measurement of refractive index profiles of fiber. An oil with arefractive index of 1.300 to 1.800 was used. A regular model was used tocalculate refractive index profile on the basis of three assumptions 1)fiber is perfectly symmetrical about center, 2) refractive index profilevaries smoothly, and 3) fiber is round.

[0102] Tensile properties were measured on an Instron machine equippedwith pneumatic cord and yarn grips which hold the yarns at the gaugelength of 10 inches. The as-wound-up yarn was then pulled by the strainrate of 10 inch/minute under standard conditions (23±2° C., 50%±5%relative humidity) and the data was recorded by a load cell. From thisdata, the stress-strain curves were obtained. Tenacity was the breakingstrength (in grams) divided by the yarn's denier.

[0103] Shrinkage was defined as an amount length contraction of a yarnon its exposure to elevated temperature. Here, shrinkage was calculatedbased on the speed difference of draw and last rolls divided by thespeed of draw rolls.

INVENTIVE EXAMPLE

[0104] Referring to FIG. 3, the dried PET pellets (IV=0.9; calculatedMV=15,310 poise at 280° C.) were fed by a Ktron “weight in loss” feederinto a counter-rotation intermeshing twin screw extruder 10 (diameter=27millimeters; length=1296 millimeters; screw=150 revolutions per minute)at feed point 12 at a rate of 12.8 pounds/hour. In the direction ofarrow 14, the pellets were forwarded by open intermeshing elements 16downstream and started to melt in close intermeshing elements 18 at thefirst zone 20 and the second zone 22. The melt was then forwarded atthird zone 24 into a compressive element 26 which acted as a dynamicseal at the end of feeding zone and gave tight compression and reducedbackflow of polymer melt and injected materials. The first feeding zonewas not heated. The temperature of the second and third zones was set at290° C.

[0105] The premixed ε-caprolactone and catalyst (tin octonate, 0.075 wt% of PET-Polycaprolactone) were injected into the extruder by a pistonpump at injection point 28 at a rate of 2.2 pounds/hour. The injectedmaterials were mixed with PET melt back and forth by two (30 millimeter)intermeshing distributive forward combing mixers 30 and 32, two (30millimeter) intermeshing distributive neutral combing mixers 34 and 36,and one (30 millimeter) intermeshing distributive reverse combing mixer38 assembled under the region of the injection point 28. A uniformmixture was then obtained in thirty seconds and forwarded into thereaction zone. The temperature of the fourth zone 40 was set at 280° C.

[0106] The reaction zone temperature through zones 42, 44, 46, and 48was set at 262° C. At this zone, in the presence of tin octonate, thePET chain extension by ring opening polymerization of ε-caprolactone wasstarted by the hydroxyl end of PET. The reaction zone consisted of two(110 millimeters) turbulators 50 and 52 which provided high percent ofextrusion volume, followed by one neutral mixer 54 which homogenized thereaction, and two (30 millimeter) turbulators 56 and 58 which providedmore contact time for the chain extension. This screw pattern allowedthe reaction to be completed in a four minute residence or reaction timeand the melt to be continuously agitated during the reaction.

[0107] The copolymerized melt was forwarded into a devolatilizing zone60 where the vacuum was set at −950 mbar. The amount of removedunreacted ε-caprolactone was 0.36 weight percent of injectedε-caprolactone.

[0108] The IV of PET-Polycaprolactone (15%) copolymer was 0.97. Thetransesterification between PET and Polycaprolactone blocks was lessthan 5%. The glass transition temperature of copolymer was 45° C., andthe melting temperature of copolymer was 231° C.

[0109] Referring to FIG. 4, the melt produced by the reactive twin screwextrusion process was fed into a spin pot 110 by a metering pump at arate of 15 pounds/hour. The temperature of melt was controlled at 260°C. The pressure at the end of extruder was 700 pounds per square inch,and the pressure in the spin pot was 1270 pounds per square inch.

[0110] The spin pot contained three layer mesh screens and a 50 roundhole spinnerette with a dimension of diameter 0.021 inch and length0.072 inch. The polymer throughtput was 2.27 grams/hole/minute with theshear rate of 2,150 sec⁻¹. The melt viscosity of PET-PCL 15% at thespinning condition (shear rate=2,150 sec⁻¹ and melt temperature=260°C.)was approximately 2,800 poise.

[0111] The extruded filaments went through a heated sleeve 112 set at280° C. and were cooled by air flow perpendicular to as-spun yarn at aflow rate of 0.13 meter/second. A water soluble spin finish was appliedat 114 to the yarn, and the yarn was taken up onto a roll 116 at a speedof 270 meter/minute to form as-spun yarn. The as-spun yarn had a radialbirefringence equal to 0.001 and denier of 3780.

[0112] The as-spun yarn was then fed onto a godet 118 heated to 60° C.at the speed of 275 meter/minute, and drawn 6.7:1 on a heated shoe 120set at 218° C. The drawn yarn was annealed on a set of rolls 122 and 124maintained at 165°C. The annealing time for the yarn was 0.2 second.

[0113] The fully drawn yarn was relaxed at 165° C. between draw and coldrolls 126 with 12% shrinkage to obtain desired stress-strain curve (FIG.2). The initial modulus of yarn was 57 g/denier, the strain at 1g/denier and 1.5 g/denier were 4% and 10%, respectively. The breakingstrength of yarn was 6.9 g/denier. The denier of each filament is 13.The initial stress barrier was 0.87 gram/denier.

[0114] All the above steps, reaction of PET with ε-caprolactone,spinning, cooling, drawing and relaxation may be carried out eitherstepwise in a discontinuous process or more advantageously as acontinuous process. The above example describes a continuous process.

[0115] The above yarn was woven and dyed into seat belt webbing. Theautomotive collision tests using a sled test showed the load limitingperformance of seat belt and the reduction of occupant injury criteria.In the sled test, the average sized dummy was restrained with seat beltwebbing and fully instrumented in a compact vehicle. The sled test wasconducted at a speed of 40 miles per hour and pulse rate of 28 g (whichis the acceleration of gravity). The movement of the dummy and injurycriteria were recorded by sensors and high speed cameras. FIG. 5illustrates the performance (with load as a function of time) of thepresent load limiting seat belt at the torso position in a vehiclecollision. Table 1 compares the performance of load limiting and PETseat belt webbings and shows the reduction of force against the occupantand improvement of injury criteria. As those skilled in the art know, inDocket 74-14: 49 C.F.R. Parts 571, 572, and 585, pulse rate meansacceleration expressed as a multiple of g (which is the acceleration ofgravity). HIC means the Head Injury Criteria. Chest mm means the chestdeflection of the vehicle occupant. Test no. Pulse Lap (kN) Torso (kN)HIC Chest (g) Chest (mm) Pelvis (g) Femur kN Inventive 28 g 6 6 436 4536.3 40 0.9/−1.4 L Example 40 mph 1.2/−0.2 R Comparative 40.5 g 8.5 9.7974 59.9 64 55.9 1.8/−4.5 L 36 mph 1.8/−1.6 R

What is claimed is:
 1. Yarn having a force-displacement profile suchthat: (a) when said yarn is subjected to an initial stress barrier offrom about 0.8 gram/denier to less than or equal to about 1.2grams/denier, said yarn elongates to less than 5 percent and has aninitial modulus in the range from about 30 grams/denier to about 80grams/denier; (b) upon subjecting said yarn to greater than said initialstress barrier and to less than or equal to about 1.5 grams/denier, saidyarn elongates further to at least about 8 percent; and (c) uponsubjecting said yarn to greater than 1.5 grams/denier, the modulusincreases sharply and said yarn elongates further until said yarn breaksat a tensile strength of at least about 6 grams/denier, wherein saidyarn comprises a multiplicity of fibers, all of said fibers havesubstantially the same force-displacement profile, and are made frompolymers having a glass transition temperature in the range from about−40° C. to about +70° C.
 2. The yarn of claim 1 wherein in part (a),said yarn elongates to less than about 3 percent.
 3. The yarn of claim 1wherein in part (a), said initial modulus ranges from about 40 to about60 grams/denier.
 4. The yarn of claim 1 wherein in part (b), said yarnelongates to at least about 10 percent.
 5. The yarn of claim 1 whereinsaid yarn is made from a block copolymer of aromatic polyester andlactone monomer and said block copolymer has a glass transitiontemperature in the range from about +20° C. to about +60°C.
 6. The yarnof claim 5 wherein said aromatic polyester is polyethyleneterephthalate.
 7. The yarn of claim 6 wherein said polyethyleneterephthalate has an intrinsic viscosity which is measured in a 60/40 byweight mixture of phenol and tetrachloroethane at 25°and is at leastabout 0.8 deciliter per gram.
 8. The yarn of claim 5 wherein saidlactone monomer is ε-caprolactone.
 9. The yarn of claim 8 wherein theamount of said ε-caprolactone is from about 10 to about 30 weightpercent of said block copolymer.
 10. A process comprising the steps of:(A) forwarding aromatic polyester melt to an injection position in atwin screw extruder wherein said aromatic polyester melt has (i) anintrinsic viscosity which is measured in a 60/40 by weight mixture ofphenol and tetrachloroethane and is at least about 0.6 deciliter/gramand (ii) a Newtonian melt viscosity which is calculated to be at leastabout 7,000 poise at 280°C.; (B) injecting lactone monomer into saidmolten aromatic polyester of said step (A); (C) dispersing said injectedlactone monomer into said aromatic polymer melt so that a uniformmixture forms in less than about thirty seconds; and (D) reacting saiduniform mixture from step (C) at a temperature from about 250°C. toabout 280° C. to form a block copolymer wherein said steps (A) to (D)occur in less than about four minutes residence time in the twin screwextruder.
 11. The process of claim 10 which additionally comprises: (E)devolatilizing said block copolymer melt to remove residual lactonemonomer.
 12. The process of claim 11 which additionally comprises thestep of: (F) injecting and dispersing ultraviolet absorber, antioxidant,pigment, and other additives into said devolatilized block copolymermelt.
 13. The process of claim 10 wherein said twin screw extruder is anintermeshing twin screw extruder.
 14. The process of claim 10 whereinsaid aromatic polyester is poly(ethylene terephthalate).
 15. The processof claim 10 wherein said lactone monomer is ε-caprolactone.
 16. Theprocess of claim 10 wherein in said step (C), said uniform mixture formsin less than about twenty seconds.
 17. The process of claim 12 whereinsaid block copolymer is chipped and the diblock copolymer chips aremelted in a single screw extruder.
 18. The process of claim 17 whereinsaid melted diblock copolymer chips are spun into fiber.
 19. Acontinuous process comprising the steps of: (A) forwarding aromaticpolyester melt to an injection position in a twin screw extruder whereinsaid aromatic polyester has (i) an intrinsic viscosity which is measuredin a 60/40 by weight mixture of phenol and tetrachloroethane and is atleast about 0.6 deciliter/gram and (ii) a Newtonian melt viscosity whichis calculated to be at least about 7,000 poise at 280° C.; (B) injectinglactone monomer into said molten aromatic polyester of said step (A);(C) dispersing said injected lactone monomer into said aromaticpolyester melt so that a uniform mixture forms in less than about thirtyseconds; (D) reacting said uniform mixture resulting from said step (C)at a temperature from about 250° C. to about 280° C. to form a blockcopolymer wherein all of said steps (A) to (D) occur in less than aboutfour minutes residence time in the twin screw extruder; (E)devolatilizing said block copolymer melt from said step (D) to removeresidual lactone monomer; (F) injecting and dispersing ultravioletabsorber, antioxidant, pigment, and other additives into saiddevolatilized block copolymer melt; (G) from the twin screw extruder andthrough a melt metering pump, metering said block copolymer melt at atemperature from about 240° C. to about 280° C. into a spin pot andextruding filaments from said spin pot equipped with a spinnerette; (H)passing said extruded filaments through a heated sleeve having atemperature from about 200° C. to about 300° C.; (I) cooling saidfilaments with ambient air wherein said air flows perpendicularly to thefilament direction at a flow rate of at least about 0.1 meter persecond; (J) applying a spin finish to said cooled filaments; (K) takingup said filaments to form a yarn on a first roll; (L) passing the yarnto a second roll having a temperature from greater than said yarn glasstransition temperature to less than said yarn crystallizationtemperature; (M) drawing the yarn between said second roll and drawrolls over a heated shoe or in a draw point localizer which ispositioned between said second roll and draw rolls and has a temperaturefrom about 180° C. to about 350° C. and then annealing the drawn yarn onsaid draw rolls having a temperature from about 140° C. to about 200°C.; (N) relaxing the drawn yarn between said draw rolls and a final rollso that the relaxed yarn has a shrinkage of about 7 percent to about 20percent; (O) cooling the relaxed yarn on the final roll set at which isat about room temperature; and (P) winding up the cooled yarn.
 20. Theprocess of claim 19 wherein said spin finish is water soluble spinfinish.
 21. The process of claim 19 wherein after said step (K), saidspun filaments have a radial birefringence of less than about 0.01. 22.The process of claim 19 wherein said draw point localizer uses steam orair.